We were discussing about one dimensional consolidation of soil. Here we will discuss about 2 D and 3 D consolidation and their occurrence both in nature or other external consolidation techniques. Consolidation phenomenon can be happened in other than wide loading area where thickness of layer is small relative to its width.
General examples are:
• Under large fill
• Beneath center of circular or square footing
• Alteration of ground water table i.e. lowering
• Beneath center of mat/raft foundation
Two dimensional consolidations:
Terzaghi provided solution for one dimensional consolidation which is extended next for two dimensional and three dimensional consolidations. Normally two dimensional consideration taken where drainage can be happened in one of the two horizontal direction with as usual in vertical. In natural condition, without providing any external consolidation drainage path, this type of consolidation is observed when strip load i.e. any narrow loading beneath which with vertical drainage, in short direction of loading some horizontal drainage is occurred.
This drainage generally happen when drainage and strain are both in vertical and any of horizontal direction. The strain may be vertical but drainage occur in both directions.
• Strip footing
Three dimensional consolidation
In this condition of consolidation drainage and consolidation are happened in three directions i.e. vertical and two horizontal directions. The strain may be in vertical but resulting drainage in three directions.
When vertical sand drains or PVD drains are used, radial drainage can be obtained. Simultaneously there will also vertical drainage. Radial drainage associated with vertical drainage reduces consolidation time abruptly. Design of sand drain will be discussed in our upcoming posts.
Effects of two dimensional and three dimensional consolidation:
The effects of 2D and 3 D consolidations are decrease in time which will help engineers to implement construction stage in short time. Now we will learn how time is reduced:
• Footing area is deceased as new drainage path introduced
• Thickness of soil layers is decreased for same cause of reducing drainage path
• Horizontal permeability of soil increased
We have published some information about sand drain you can read this for reference radial drainage.